(a) Field of the Invention
The present invention relates to novel disazo compounds, a process for the preparation of same, and an application of said disazo compounds and analogues thereof to electrophographic sensitive materials.
(b) Description of the Prior Art
It is known that some organic compounds are useful as a photoconductive material for preparing photosensitive materials for use in the electrophotographic process. The "electrophotographic process" herein is one of the image-forming processes which generally comprises first charging a photoconductive sensitive material with electricity by corona discharge or the like in the dark, subsequently subjecting it to image-wise exposure so as to discharge the electric charge of the exposed area selectively, thereby obtaining an electrostatic latent image, and then rendering visible this latent image by a developing means employing a developer, thereby forming an intended image. As the fundamental characteristics required for the photosensitive materials for use in the electrophotographic process, there are enumerated (1) an appropriate chargeability in the dark, (2) a low dischargeability in the dark, and (3) a rapid dischargeability with exposure to light.
As a matter of fact, however, the known organic photoconductive compounds have not always sufficiently satisfied these requirements. As applicable photoconductive materials, there are known, inorganic materials such as selenium, zinc oxide, etc., organic materials such as indigo-type compounds, phthalocyanine-type compounds, etc., of which selenium has admittedly been widely put to practical use. However, with adoption of various electrophotographic processes, there is an increasing demand for a photosensitive material suitable to any of these processes, that is, a demand for, for instance, a belt-shaped photosensitive material or the like having the aforementioned fundamental characteristics as well as a satisfactory flexibility with respect to the shape thereof. In this regard, selenium is generally difficult to form into a photosensitive material having such a shape as above.
Meanwhile, as electrophotographic sensitive materials prepared by forming a photosensitive layer containing some azo pigment, as an effective ingredient, on a conductive support, one prepared by employing monoazo pigment (cf. Japanese Pat. No. 16474/1969) and one prepared by employing benzidine type disazo pigment (cf. Japanese Pat. Open No. 37543/1972) are well known. These azo pigments are admittedly useful materials as an effective ingredient of the photosensitive layer as stated above, but when various requirements for photosensitive materials are taken into account from the viewpoint of the electrophotographic process, there has in fact not yet been obtained such a material as will sufficiently meet these requirements. Therefore, it is a matter of more importance to provide a wide variety of pigments, not limited to azo pigments, so as to afford a wide range of selection of pigments acting as an effective ingredient, thereby rendering it possible to provide a photosensitive material apposite to any specific process. In other words, it is desirable for the electrophotographic process that the variety of the pigments workable as an effective ingredient of photosensitive materials is as wide as possible.
A primary object of the present invention is to provide novel disazo compounds which are free from the drawbacks possessed by the photoconductive substances employed for the above described photosensitive materials and are especially useful as a photoconductive material, as well as a process for the preparation of said compounds.
A secondary object of the present invention is to provide electrophotographic sensitive materials having a high sensitivity as well as a high flexibility which materials contain a disazo pigment, said disazo pigment being selectable from a great variety and being useful as an effective ingredient in various electrophotographic processes.